DS-72-40 Datasheet, PDF (14/17 Pages) Cymbet Corporation – EnerChip™ CC Energy Harvester Evaluation Kit

CBC-EVAL-10B EnerChip CC EH Evaluation Kit
Using Other Energy Harvesting Transducers
CBC-EVAL-10B includes a standard amorphous silicon solar panel (Sanyo AM1815 type) configured as 8 series-
connected cells on a glass substrate. The output voltage and current vary with incident light intensity, wave-
length, and load impedance.
DC sources other than the PV cell provided with the CBC-EVAL-10B may also be used as the energy harvesting
power transducer. The CBC-EVAL-10B module has an overvoltage protection circuit to clamp the input voltage
to less than 3.4V which protects the CBC-EVAL-10B and any loads attached to it from overvoltage conditions
on the input transducer which otherwise may exceed 7 volts. The protection circuit will clamp input currents of
up to 2mA so additional protection may be needed with very high power. The minimum input voltage required
to activate the internal charge pump of the CBC3150 is 2.5V. At <2.5V, the EnerChips will not charge and the
power management circuit will not function. It is recommended that the input power source have a maximum
power operating point as close to 3.0V as possible. Operating characteristics for most transducers are typically
available from the manufacturer’s data sheet. An example photovoltaic cell operating curve is shown below.
Output impedance, operating voltage, and peak power point can also be verified by empirical measurements.
To determine the peak power point of a given PV cell, measure the load voltage and current as a variable load
impedance across the transducer is swept over a broad enough range where the peak power point can be
found by finding the maximum product of the measured load voltage and current.
Current-Voltage Curve
VOC: Open-circuit voltage
ISC: Short-circuit current
VOP: Optimum operating voltage
IOP: Optimum operating current
PMAX: Maximum operating power
Once the peak power point of the PV cell has been determined, the CBC3150 operating point can be adjusted
to match the PV cell. This is done by choosing different POR circuits with appropriate switching voltages and
adding a resistor divider R2 and R3 to the CBC-EVAL-10 module. As shipped, those resistors are not populated.
Cut the solder trace in the R2 location prior to adding the resistor. Resistor values should be sized according
the guidelines in the CBC3150 data sheet. It is important to note that the resistor divider will present a per-
manent parasitic load to the PV cells and therefore the calculation should be made to determine whether the
standard CBC3150 impedance matching setpoint of ~3V - though it might not be at the peak power point of a
particular PV cell - is preferred to the more optimized setpoint when considering the additional parasitic load on
the PV resulting from the added resistor divider.
©2014 Cymbet Corporation • Tel: [phone] • www.cymbet.com
DS-72-40 Rev C

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